Golf ball manufacturers have been experimenting with various materials and manufacturing methods for golf balls over the years in an attempt to improve overall performance and durability and to further refine the manufacturing process.
For example, a ball that includes at least one cover layer formed from an ionomeric resin is popular design among golf ball manufacturers due to the durability and performance characteristics (including scuff resistance and rebound) associated with the material. However, the recent trend toward light stable cover materials such as aliphatic polyurethane and polyurea has introduced durability and adhesion issues, particularly when the inner cover layer is formed from an ionomer resin and the outer cover layer is formed from polyurethane or polyurea. In an effort to remedy this issue, the inner components of most commercially available polyurethane- or polyurea-covered golf balls are surface treated, e.g., corona discharge/silane dipping, to overcome the adhesion problems. The surface treatment, however, adds cost and time to the manufacturing process.
Some manufacturers have attempted to use highly neutralized polymers in place of the typical cover layer materials, i.e., inner and outer cover layers, in an attempt to overcome the problems addressed above. Potential compatibility issues remain with these fatty acid-based highly neutralized polymers, such as those discussed in U.S. Pat. No. 6,329,458, however, due to their hydrophobic backbone moiety. For example, the fatty acids may vaporize during injection molding, generating a large amount of gas, which may lead to molding defects, including adhesion problems. In particular, when such a highly neutralized polymer is used as an inner cover layer with a polyurethane or polyurea cover layer disposed thereon, the highly neutralized polymer behaves like soap and prevents the materials of the outer cover layer from properly adhering to the inner layer. In addition, the presence of this gas may also result in gas constituents settling on the surface of the molded object, which greatly lowers the paintability or post-processing options.
There are many examples of such incompatibility between layers due to the materials used therein, which, at a minimum, affect the adhesion between the layers, and ultimately affect the performance of the ball. In fact, numerous materials have beneficial qualities to golf ball manufacturers, but, because of certain detrimental qualities, these materials cannot be used independently of other more conventional materials. For example, a material with poor moisture resistance, poor durability, or low resiliency would not be useful on its own to form a layer of a golf ball. These type of materials are generally blended with other materials or not used at all.
Thus, a need exists in the golf ball art to find a way to use materials typically discounted for golf ball layers in a way that capitalizes on the beneficial nature of the material while at the same time minimizing or completely overcoming the detrimental qualities. In addition, a need exists for a method to partner complimentary, but typically incompatible, materials in adjacent golf ball layers sans the use of conventional surface treatment options to produce a golf ball with excellent layer adhesion and improved performance characteristics. As such, it would be advantageous to form a hybrid golf ball component or, in other words, a layer construction that mechanically bonds to otherwise incompatible layers together.